Field of the Invention (Technical Field)
The present invention relates to the field of a method of magnetization reversal, time stable ferrimagnetic material, a product and a domain comprising said material, a system for magnetization reversal, and information storage.
Description of Related Art
In physics, a ferrimagnetic material is one in which magnetic moments of the atoms on different sublattices are opposed, as in antiferromagnetism; however, in ferrimagnetic materials, the opposing moments are unequal and a spontaneous magnetization remains. Such occurs when the sublattices consist of different materials or ions (such as Fe2+ and Fe3+).
Ferromagnetism is exhibited by, e.g., ferrites and magnetic garnets.
Ferrimagnetic materials are like ferromagnets in that they hold a spontaneous magnetization below their Curie temperature, and show no magnetic order (are paramagnetic) above this temperature. However, there is sometimes a temperature below the Curie temperature at which the two sublattices have equal moments, resulting in a net magnetic moment of zero; this is called the magnetization compensation point. This compensation point is observed easily in garnets and rare earth-transition metal alloys (RE-TM). Furthermore, ferrimagnets may also exhibit an angular momentum compensation point at which the angular momentum of the magnetic sublattices is compensated. This compensation point is a crucial point for achieving relatively high speed magnetization reversal. It is noted that the materials are currently not intended for use in prior art devices.
Processes of magnetization reversal triggered by a stimulus shorter than the time of thermal equilibration (100 ps) is a topic of intense research interest in both fundamental and applied magnetism.
It is generally accepted that magnetization reversal should be driven by a stimulus represented by a polar or axial vector such as magnetic field, electric current, electric field or cross-product of two electric fields.
For data storage magnetic systems should be time stable, in order not to lose data over a very long period of time, e.g., in the order of years, such as ten or more years.
Even further magnetic materials should be stable, i.e. not change spin, in relatively strong external magnetic fields applied to these materials, e.g., by chance.
Also, e.g., for data storage, a density of magnetic domains, to be addressed, should be high, e.g., in the order of Gb/cm2 or higher.
It is noted that a combination of various requirements is often even more difficult to achieve, as for instance smaller domains tend to be less stable. A high density system is, e.g., therefore difficult to obtain.
On the other hand, magnetic materials should change their magnetic moment rapidly, e.g., when applying a stimulus to change the magnetic moment in order to store data. Preferably such change should take place at a speed comparable to processor speed of a modern computer, e.g., at a rate in the order of Gb/sec or larger. Present systems are typically limited to about 0.1-0.5 Gb/sec, which is regarded as relatively slow, especially in comparison to processor speed.
Even further, changes of magnetic moment should be achievable at relatively low energy consumption, in order to limit energy consumption of a computer. Such implies amongst others that heat should not be applied, or at the most at a low level.
Further, such heat assisted change of magnetic moment is not preferred in view of durability and stability of, e.g., magnetic material used, as too much heat may, e.g., deteriorate material.
Also, it should preferably be relatively easy to change a magnetic moment, such as using state of the art techniques.
Thereto new methods of magnetization reversal as well as magnetic materials need to be developed.
Radu et al. in Nature, part 472, nr. 7342, p. 205-208 (14 Apr. 2011), Radu et al. in Nature, (30 Mar. 2011), p. 1-9 and Koopmans et al. in Nature Materials, (Jan. 1, 2009) describe magnetization reversal by applying a stimulus in the presence of an external electro-magnetic field, as it was considered necessary to apply both in combination in order to achieve magnetization reversal.
Even further, as many existing materials are not suited for such magnetization reversal, and/or do not fulfill further requirements, amongst others mentioned throughout the description, a new class of magnetic materials needs to be developed.
The present invention is aimed at a method for magnetization reversal, at magnetic materials, and applications thereof, which overcome one or more of the above disadvantages, without jeopardizing functionality and advantages.